Change set precedence api to return an error message.

stepmania/src/arch/InputHandler/InputHandler_Carbon.cpp

@@ -47,8 +47,11 @@ int InputHandler_Carbon::Run( void *data )
 	CFRetain( This->m_LoopRef );
 	
 	This->StartDevices();
-	SetThreadPrecedence( 1.0f );
-
+	{
+		const RString sError = SetThreadPrecedence( 1.0f );
+		if( !sError.empty() )
+			LOG->Warn( "Could not set precedence of the input thread: %s", sError.c_str() );
+	}
 	// Add an observer for the start of the run loop
 	{
 		/* The function copies the information out of the structure, so the memory pointed

stepmania/src/arch/Sound/RageSoundDriver_AU.cpp

@@ -194,7 +194,9 @@ int64_t RageSoundDriver_AU::GetPosition() const
 void RageSoundDriver_AU::SetupDecodingThread()
 {
 	/* Increase the scheduling precedence of the decoder thread. */
-	SetThreadPrecedence( 0.75f );
+	const RString sError = SetThreadPrecedence( 0.75f );
+	if( !sError.empty() )
+		LOG->Warn( "Could not set precedence of the decoding thread: %s", sError.c_str() );
 }
 
 float RageSoundDriver_AU::GetPlayLatency() const

stepmania/src/archutils/Darwin/DarwinThreadHelpers.cpp

@@ -3,8 +3,6 @@
 #include <mach/mach_init.h>
 #include <mach/mach_error.h>
 #include "Backtrace.h"
-#include "RageLog.h"
-#include "RageUtil.h"
 
 bool SuspendThread( uint64_t threadHandle )
 {
@@ -53,18 +51,17 @@ bool GetThreadBacktraceContext( uint64_t iID, BacktraceContext *ctx )
 #endif
 }
 
-void SetThreadPrecedence( float prec )
+RString SetThreadPrecedence( float prec )
 {
 	// Real values are between 0 and 63.
-	if( CLAMP(prec, 0.0f, 1.0f) )
-		LOG->Warn( "Thread precedence clamped to %f.", prec );
+	DEBUG_ASSERT( 0.0f <= prec && prec <= 1.0f );
 	thread_precedence_policy po = { integer_t( lrintf(prec * 63) ) };
 	kern_return_t ret = thread_policy_set( mach_thread_self(), THREAD_PRECEDENCE_POLICY,
 					       (thread_policy_t)&po, THREAD_PRECEDENCE_POLICY_COUNT );
 	
 	if( ret != KERN_SUCCESS )
-		LOG->Warn( "Couldn't set the precedence for the input thread: %s",
-			   mach_error_string(ret) );
+		return mach_error_string( ret );
+	return RString();
 }
 	
 /*

stepmania/src/archutils/Darwin/DarwinThreadHelpers.h

@@ -5,7 +5,7 @@ bool SuspendThread( uint64_t threadHandle );
 bool ResumeThread( uint64_t threadHandle );
 uint64_t GetCurrentThreadId();
 // Valid values are from 0.0f to 1.0f. 0.5f is default.
-void SetThreadPrecedence( float prec );
+RString SetThreadPrecedence( float prec );
 
 #endif